Winter tick sharing between ungulates in the Greater Yellowstone Ecosystem and implications for apparent competition

Authors: KOSER, TROY - Montana State University; MARTIN, ALYNN - Texas A&M University; COURTEMANCH, ALYSON - Wyoming Department Of Game & Fish; THOMPSON, LAURA - Us Geological Survey (USGS); WISE, BENJAMIN - Wyoming Department Of Game & Fish; FRALICK, GARY - Wyoming Department Of Game & Fish; DEWEY, SARAH - Us National Park Service; GIRARD, AMY - Us Fish And Wildlife Service; SCURLOCK, BRANDON - Wyoming Department Of Game & Fish; ROGERSON, JARED - Wyoming Department Of Game & Fish; Oyen, Kennan; CROSS, PAUL - Us Geological Survey (USGS)

Submitted to: Ecosphere
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/3/2024
Publication Date: 1/22/2025
Citation: Koser, T., Martin, A., Courtemanch, A., Thompson, L., Wise, B., Fralick, G., Dewey, S., Girard, A., Scurlock, B., Rogerson, J., Oyen, K.J., Cross, P. 2025. Winter tick sharing between ungulates in the Greater Yellowstone Ecosystem and implications for apparent competition . Ecosphere. 16(1). Article 70129. https://doi.org/10.1002/ecs2.70129.
DOI: https://doi.org/10.1002/ecs2.70129

Interpretive Summary: Winter ticks are a single host tick that causes mortality in moose. Whether other hosts (elk, deer, or sheep) can act as a reservoir for these ticks is unknown. To test the role of tick-sharing in winter tick infestations on moose, we used genetic analysis to compare population-level differences among ticks collected on moose and those from elk. We found that there was little genetic difference between ticks from these two host types but there were large genetic differences across relatively short geographic distances. This could suggest that elk are a good reservoir host for ticks and should be considered in tick management strategies.

Technical Abstract: Host species heterogeneity can drive parasite dynamics through variation in host competency as well as host abundance. We explored how elk (Cervus canadensis) with apparent subclinical infestations of winter tick (Dermacentor albipictus) may be a cryptic reservoir and drive winter tick dynamics, impacting moose (Alces alces) populations. We found that winter tick infestation loads did not vary remarkably between both host species and winter ticks sourced from elk and moose produced similar numbers of larvae which activated within five days of each other. We also found similar larval densities in habitats predominately used by elk, moose, and both host species. Our analysis of 2,793 informative single nucleotide polymorphisms showed genetic differentiation among tick populations that were only ~75 km apart, but fewer differences among ticks from elk or moose in the same locality, suggesting sharing of winter ticks across host species. Despite the clinical signs of high winter tick infestations being most apparent on moose, elk may be critical drivers of winter tick population dynamics in areas where they vastly outnumber moose populations, a common characteristic of ungulate communities in western North America. Management interventions aimed at addressing winter tick issues on moose may wish to consider the movement patterns and abundance of cryptic reservoirs like elk.